We present the morphology and stellar population of 27 \textcolor blackextremely metal poor galaxies ( EMPGs ) \textcolor blackat z \sim 0 with metallicities of 0.01 - 0.1 Z _ { \odot } .
We conduct multi-component surface brightness ( SB ) profile fitting for the deep Subaru/HSC i -band images of the EMPGs with the Galfit software , carefully removing the SB contributions of potential associated galaxies ( PAGs ) .
We find that the EMPGs \textcolor blackwith a median stellar mass of \log ( M _ { * } / { M } _ { \odot } ) = 5.77 have a median Sérsic index of \textcolor black n = 1.08 and a median effective radius of \textcolor black r _ { e } = 176 pc , suggesting that typical EMPGs \textcolor blackare very compact disk galaxies .
We compare \textcolor blackthe EMPGs with z \sim 6 galaxies and local galaxies on the size-mass ( r _ { e } – M _ { * } ) diagram , and identify that the majority of the EMPGs have a r _ { e } – M _ { * } relation similar to z \sim 0 star-forming galaxies rather than z \sim 6 galaxies .
Not every EMPG is a local analog of high- z young galaxies in the r _ { e } – M _ { * } relation .
We also study the PAGs of our galaxies , and find that \textcolor black23 out of the 27 EMPGs show detectable PAGs within the projected distance of 10 kpc .
The PAGs have median values of \textcolor black n = 0.93 , r _ { e } = 1.41 kpc , and \log ( M _ { * } / { M } _ { \odot } ) = 7.47 that are similar to those of local \textcolor blackdwarf irregulars and ultra-diffuse galaxies .
A spectrum of one EMPG-PAG system , so far available , indicates that the PAG is dynamically related to the EMPG with a median velocity difference of \Delta V = 96.1 km s ^ { -1 } .
This moderately-large \Delta V can not be explained by the dynamics of the PAG , but likely by the infall on the PAG . \textcolor blackEMPGs may form in infalling gas , and become part of PAG disks \textcolor blackundergoing further metal enrichment .